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Europa’s dark lines may be due to irradiated salt

Jupiter's moon Europa has a puzzling and intriguing surface as seen in this reprocessed color view, made from images taken by NASA's Galileo spacecraft in the late 1990s. Photo Credit: NASA/JPL-Caltech/SETI Institute

SpaceFlight Insider

May 17th, 2015

NASA released data this week from recent laboratory experiments further indicating Jupiter’s moon Europa could contain a subsurface ocean and possibly even support life. Europa, the smallest of the four Galilean moons, contains surface features covered by an intriguing dark material. The data shows the enigmatic dark streaks are likely formed as a result of sea salt discolored from exposure to radiation. The presence of surface sea salt could mean the ocean is interacting with the seafloor, boosting the notion that it may be hospitable to life.

“We have many questions about Europa, the most important and most difficult to answer being is there life? Research like this is important because it focuses on questions we can definitively answer, like whether or not Europa is inhabitable,” said Curt Niebur, Outer Planets Program scientist at NASA Headquarters in Washington. “Once we have those answers, we can tackle the bigger question about life in the ocean beneath Europa’s ice shell.”

A salt sample inside a JPL test chamber is bathed in an eerie blue glow as an electron beam scans across it many times each second, delivering a powerful dose of radiation. (Click to enlarge.) Photo Credit: NASA/JPL-Caltech

The nature of the dark material covering the linear surface fractures and other geological features on the Europa’s surface has puzzled scientists for well over a decade. The dark material covers younger features on Europa’s surface, and as such is thought to have erupted from inside the moon, but with very little data available, scientists could not determine the chemical composition of the dark material.

One thing scientists know for sure is that Europa is constantly bombarded by radiation from Jupiter’s mighty magnetic field. Electrons and ions are constantly slammed into the moon’s surface, much like particles slam together inside a particle accelerator such as the Large Hadron Collider (LHC). This process contributes to the dark color of the fractures on Europa.

Prior studies utilized data from NASA’s Galileo spacecraft, along with other telescopes, to hypothesize that the surface discolorations were attributed to sulfur and magnesium compounds. Results showed the irradiated sulfur compounds could be responsible for some of the discolorations; however, the new study indicated irradiated salts were behind the discoloration within Europa’s youngest surface features.

“If it’s just salt from the ocean below, that would be a simple and elegant solution for what the dark, mysterious material is,” said research lead Kevin Hand, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California.

A “Europa-in-a-can” laboratory set-up at NASA-JPL mimics conditions of temperature, near vacuum, and heavy radiation on the surface of Jupiter’s icy moon Europa. (Click to enlarge.) Photo Credit: NASA/JPL-Caltech

So how did scientists figure out these dark surface stripes? Hand and his colleague Robert Carlson used what they call “Europa in a can”. Basically, they created a simulated Europa in their lab’s test apparatus. They tested possible candidate substances and collected spectra – a.k.a. chemical fingerprints – which are hidden in the light reflected by the individual compounds.

“We call it our ‘Europa in a can’,” Hand said. “The lab setup mimics conditions on Europa’s surface in terms of temperature, pressure and radiation exposure. The spectra of these materials can then be compared to those collected by spacecraft and telescopes.”

A close-up of salt grains discolored by radiation following exposure in a “Europa-in-a-can” test setup at JPL. Photo Credit: NASA/JPL-Caltech

In this study, the team tested samples of common salt (sodium chloride), as well as mixtures of salt and water, within a vacuum chamber acclimated to Europa’s chilly minus 280 degrees Fahrenheit (minus 173 degrees Celsius) surface temperature. The team then blasted the salty samples with beams of electrons in order to simulate the radiation blasts the moon’s surface is subjected to.

In the lab, tens of hours of radiation exposure are roughly equivalent to a century on Europa. The salty samples started out white, just like table salt, but turned a yellow-brown color from the radiation. The spectral analysis showed that the colors produced in the lab were very similar to the colors of the surface features in the Galileo mission’s images.

“This work tells us the chemical signature of radiation-baked sodium chloride is a compelling match to spacecraft data for Europa’s mystery material,” Hand said.

The team discovered that the longer the samples were exposed to radiation, the darker the color of the surface features. The team thinks the color variation can help determine the age of the various geologic features as well as any material ejected from Europa’s surface plumes.

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Reader Comments

Space exploration has a friend in Congressman John Culberson. He is completely fascinated with the possibility of life on Europa.

Ocean moons of the gas giants like Europa are not a real popular subject with NewSpace fans. They make Mars look bad in comparison as a place to explore. The atomic bomb propelled spaceships necessary to get to these icy bodies would have to be assembled and tested on the Moon or in lunar orbit. And of course such spaceships are far beyond the means of “entrepreneurs.”

The submersibles that would be used to explore these underwater worlds had their own era just like Apollo. The popular reference for these subs by Busby is available in several places online. Really interesting engineering and buoyancy system information for any future Europa sub pilots.

If you want it to be a humans and not robots Byron then it will require going to the Moon with the SLS. About 10 years of 6 to 8 launches a year would result in several nuclear propelled spaceships each with a thousand tons or so of lunar ice derived water for cosmic ray shielding. Nuclear pulse propulsion would take a spaceship to Europa in about a year and require a couple thousand bombs for a round trip. Definitely need a massive water shield not only for cosmic rays but also for Jupiter’s radiation belts.

A spaceship could land on Europa, melt a tunnel straight down in which to launch the sub with a trashcan nuclear reactor, and the crew could stay inside the spaceship 14 feet thick water shield up until dropping the sub down the shaft- and would then be protected from the radiation by the ice.

I wrote an article in 2011 describing the basic concept and an abridged version was published in Space Safety Magazine. Here is the complete version: enjoy

Bandyetagin, just to clarify, I support a robotic mission. It seems to me that for the cost of a manned mission to Europa, you could send robots to Europa, Enceladus, Titan and probably a dozen or so other worlds.

Some people support space probes, some people support LEO tourist space stations, some people support Mars missions, some people support cloud cities on Venus, some people support getting rid of NASA and handing it all over to Musk.

And some people support going back to the Moon and exploiting the critical enabling resources there to expand the human presence into the solar system. Until space advocates line up behind going back we will go nowhere and remain where we have since 1972. Just to clarify my view.

Very encouraging for me to see that as a comment on a space forum.
Thank you Byron. It gets lonely out here.

If you make comments like that on most of the space discussion boards you will find out exactly why I have that user name. Unless you are more tolerant of being insulted and endlessly harassed and can control your temper better than me. The NewSpace mob does not allow criticism of Musk or SpaceX and immediately tries to shut down any comments supporting SLS or returning to the Moon. Bypassing LEO with Super Heavy Lift Vehicles dumps their business plan in the trashcan. Almost all of us who disagree with their agenda stopped saying so years ago because of the cyberthuggery.

As SLS progresses and more and more people start advocating going back to the Moon these forums are going to feature some very unhappy NewSpace fanboys.

Bandyetagin, I too support SLS, and consider the cancellation of Constellation to have been a disaster of the first magnitude. I thought (and still think) that the two booster solution (Ares I for crew and Ares V for cargo) was a simple and elegant solution to allow a much greater total lift without being cost-prohibitive.

Screaming at the top of their lungs about how horribly expensive Constellation was has become the big lie to the public. The truth is that you get what you pay for and there is no cheap. Separating the crew and cargo vehicles resulted from the lessons taught by the Space Shuttle.

The greatest disaster in my view was not going with Sidemount. Shannon had the solution and we would be flying it right now 8 times a year. I get sad every time I think about it.